nullpointerexception - Weird Java Null Pointer Exception when writing to XML File -

i wrote code write movies array list in xml file based on tutorial page here

here code written in repository:

    public void writemoviestoxml() {     system.out.println("null");      try{         documentbuilderfactory dbfactory = documentbuilderfactory.newinstance();         documentbuilder dbuilder = dbfactory.newdocumentbuilder();         document doc = dbuilder.newdocument();          element rootelement = doc.createelement("repo");         doc.appendchild(rootelement);          element movie = doc.createelement("movie");         rootelement.appendchild(movie);          (int i=0; i<moviemap.getmoviemap().size(); i++)         {             attr attr1 = doc.createattribute("title");             attr1.setvalue(moviemap.getmoviemap().get(i).gettitle());             attr attr2 = doc.createattribute("renttimes");             if(moviemap.getmoviemap().get(i).getrenttimes() == null)                 system.out.println("null");             attr2.setvalue(moviemap.getmoviemap().get(i).getrenttimes().tostring());         }          transformerfactory transformerfactory = transformerfactory.newinstance();         transformer transformer = transformerfactory.newtransformer();         domsource source = new domsource(doc);         streamresult result = new streamresult(new file("c:\\users\\ruspauladrian\\desktop\\lab2_4\\movies.xml"));         transformer.transform(source, result);          streamresult consoleresult = new streamresult(system.out);         transformer.transform(source, consoleresult);      } catch (exception e)     {         e.printstacktrace();     } } 

and here code in ui exception:

system.out.println("bye bye"); repository.writemoviestoxml(); 

the code @ end of program (hence "bye bye"). want program close after saving changes. have tried debugging "null" println in first code part never sees @ loss why code producing problem without entering function.

here imports used in repository if helps:

import datastructures.moviemap; import datastructures.peoplelist; import domain.movie; import org.w3c.dom.*; import javax.xml.parsers.documentbuilder; import javax.xml.parsers.documentbuilderfactory; import javax.xml.transform.transformer; import javax.xml.transform.transformerfactory; import javax.xml.transform.dom.domsource; import javax.xml.transform.stream.streamresult; import java.io.file; 

it seems repository null, did initialize repository first?

repository repository = new repository(); repository.writemoviestoxml(); 

you can make method writemoviestoxml static , point class.

repository.writemoviestoxml();